How much files I can upload to Adobe stock in one day?

It is very time consuming to add useful titles and appropriate keywords, and this effort is the most important one in getting your images noticed and sold once they're in the database. Of course, image quality and uniqueness counts too. If you haven't previously uploaded to Adobe, go slow. Submit 6-10 images, wait for Moderator feedback, re-edit any rejected images if possible and resubmit. In this manner, you'll learn what quality level Adobe is looking for and become more experienced at assessing your images for suitability.

You are going to get several worn out reviewers who maybe will just start rejecting. Maybe. ;-))
I believe a continuous uploading may help photo placement because the photos are marked as new media.

But I am not sure.

Yes! But I wouldn't recommend it. If you get a lot of rejections, it can be harder to determine what was wrong with the file.